CG these vst don't have a gui so they depend on their host to provide it for them, that is the reason they don't work on their own in RW. You will need something like a multifx vst to load these dll and that will provide the interface for these.
Other than that you can try this. :http://requietus.blogspot.com/2008/12/simulanalog-guitar-suite-gui.html
seems someone has made the gui version for these.
I havent tried them yet though. (i do have an old jvm900 gui version of the dll )
btw the simulanalog JCM 900 is one of the best simulation for that particular marshall model.

Seems there is a new Commercial vst coming up from them too :
http://www.overloud.com/
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